1. Field of the Invention
The present invention relates to an Fe-Cr-Al steel which is superior in workability, oxidation resistance, corrosion resistance and economy. More particularly, the present invention is concerned with an Fe-Cr-Al steel suitable for use as a material of members or structural parts which are subjected to a strong oxidizing environment or hot oxidizing atmosphere, e.g., parts of internal and external combustion systems, exhaust systems, boilers, incinerators and so forth.
2. Description of the Related Art
An oxidation resistant Fe-Cr-Al steel is disclosed in Japanese Patent Laid-Open Publication No. 63-45351 and also in the specification of U.S. Pat. No. 4,414,023. This steel contains 8 to 25 wt% of Cr and 3 to 8 wt% of Al. When this steel is used in a hot oxidizing atmosphere, Al in the steel is preferentially oxidized to form a fine protective film of Al.sub.2 O.sub.3 so as to exhibit high resistance to oxidation. This oxidation resistant steel, therefore, is suitable for use in components of combustors or the like.
This known Fe-Cr-Al oxidation resistant steel, however, is still unsatisfactory from the view point of workability because, in general, the toughness of this steel is reduced when the Al content exceeds 3 wt%, with the result that surface defects are often caused during hot rolling. Surface grinding has to be conducted repeatedly to remove such surface defects.
In addition, sheets of this known steel tend to be ruptured when subjected to cold rolling. The rolling of this steel, therefore, has to be conducted at a low speed and reduction while elevating the temperature of the sheet.
Toughness of the steel can be improved by reducing the contents of Cr and Al as proposed in Japanese Patent Publications Nos. 54-35571 and 55-41290. Reduction of the Cr and Al contents, however, undesirably reduces the oxidation resistance to make the steel materially unusable at high temperatures exceeding 1000.degree. C.